I'm glad you were able to reproduce this.
I don't use Diffzilla very often but it does have a couple of "killer features" that Beyond Compare (my favorite diff utility) doesn't have. These are the ability to compare by symbol (e.g., functions) and by line ranges. I often use Beyond Compare's clipboard compare feature as an easier to use analog to SE's line range compare but it doesn't have any link to the original files so, obviously, you can't edit and save changes when using that feature.
I hope that, now that this is reproduced, it won't be difficult to fix.